20 weeks - from babycenter

How your baby's growing: Your baby weighs about 10 1/2 ounces now. She's also around 6 1/2 inches long from head to bottom, and about 10 inches from head to heel. (For the first 20 weeks, we use measurements taken from the top of the baby's head to her bottom — known as the "crown to rump" measurement. After that, we use measurements from head to toe. This is because a baby's legs are curled up against her torso during the first half of pregnancy and are very hard to measure.)A greasy white substance called vernix caseosa coats her entire body to protect her skin during its long submersion in amniotic fluid. (This slick coating also eases the journey down the birth canal.)Your baby is swallowing more, which is good practice for her digestive system. She's also producing meconium, a black, sticky substance that's the result of cell loss, digestive secretion, and swallowed amniotic fluid. This meconium will accumulate in her bowels, and you'll see it in her first messy diaper (although a few babies pass it in utero or during delivery).

How your life's changing: You've made it to the halfway mark — Congratulations! The top of your uterus is at the level of your belly button now, and you've likely gained about 10 pounds. Expect to gain an average of about another pound each week from now on. (If you started your pregnancy underweight, you may need to gain a bit more; if you were overweight, perhaps a bit less.) Make sure you're getting enough iron, a mineral that's used primarily to make hemoglobin (the part of your red blood cells that carries oxygen). During pregnancy, your body needs more iron for your developing baby and the placenta, and to keep up with your expanding blood volume. Iron-rich foods include lean red meat, poultry, fish, lentils and other legumes, spinach, and iron-fortified cereals.If you haven't already signed up for a childbirth education class, you may want to look into one. Whether you're a first-timer or a pro, you can benefit from a structured class that helps prepare you for the rigors of labor and delivery. Most hospitals and birth centers offer classes, either as weekly meetings or as a single intensive, all-day session. Ask your doctor or midwife for a recommendation. At 37 weeks, you'll be considered full-term, so plan to be done with classes by then.